1. Field of the Invention
The present invention relates to a ratchet device for effecting intermittent rotation of a ratchet wheel, and more particularly to such a ratchet device which is capable of controlling a rotating angle of the wheel with improved angular positioning accuracy. The present invention is also concerned with a tape feeding apparatus which includes such a ratchet device.
2. Discussion of the Prior Art
The ratchet device as described above generally includes: (a) a body; (b) a ratchet wheel rotatably supported by the body and having teeth; (c) a feed pawl having an engaging portion engageable with the teeth of the ratchet wheel; (d) a support member movably supported by the body, for movably holding the feed pawl such that the engaging portion is movable in a direction toward and away from the teeth of the ratchet wheel; (e) biasing means for biasing the feed pawl toward the teeth of the ratchet wheel for engagement of the engaging portion with the teeth; and (f) drive means for moving the support member between a first position for placing the feed pawl in a fully advanced position, and a second position for placing the feed pawl in a fully retracted position. In the thus constructed ratchet device, when the support member is moved from the second position to the first position, the feed pawl is advanced so that its engaging position passes or clicks past at least one of the teeth of the ratchet wheel. When the support member is moved from the first position to the second position, the feed pawl is retracted while engaging the last one of the above-indicated at least one tooth which the engaging portion has passed last, so as to rotate the ratchet wheel a predetermined angle corresponding to the number of the above-indicated at least one tooth. The number of the teeth the engaging portion of the feed pawl passes during one stroke of the support member is determined by the distance of the movement of the support member, which in turn is determined depending upon a desired rotating angle of the ratchet wheel.
The ratchet device constructed as described above may be used for intermittently rotating a rotary member about an axis thereof by a predetermined incremental angle at a time, or intermittently moving a linearly movable member by a predetermined incremental distance at a time. For example, the ratchet device is used for intermittently feeding a carrier tape which has a substrate having pockets receiving electronic components, and a covering film for covering the substrate so as to close the pockets. In this case, the ratchet device serves to intermittently rotate a sprocket wheel whose teeth are adapted to engage feed holes or perforations formed through the carrier tape.
In the known ratchet device as described above, however, the ratchet wheel tends to be excessively rotated due to the inertia thereof or that of the movable member connected to the ratchet wheel when the support member is moved from the first position to the second position to rotate the ratchet wheel. Consequently, the movable member is moved more than the predetermined or nominal distance.